Graphitic steel of controllable hardenability and article made therefrom



Aug. 22; 1950 2,519,627

F. R. BONTE v GRAPHITIC STEEL F CONTROLLABLE HARDENABILITY AND ARTICLE .MADE THEREFROM Filed March 20, 1948 32 34 36 B 40 I DISTANCE FROM QUENCHED END OF $PECIMEN,$IXTEENTH$ 0F INCH s'raal. a

STEEL A I) O 0 O O O 3 his Q7 7' OR/VE 715".

n INVENTOR. Fezozezcx A. flow-5;

Patented Aug. 22, 1950 ems STAT-Es PATENT OFFICE G RA'PHIT IG STEEL OF CONTBOLLABLE HARDENABILfITY AN D-ARTICLE MADE THEREFROM' Erede ickfllt."BontenGan n; Ohio, assignorfto"The. TimkenRoiletBcaring Company, Ca ntn,10hio,

' ,a corporation of Oh'io n catiaalviarehec, 194s, SeriaL-No.16,006

This inventim relates to graphitic steels, and

this applicatiomisa continuation-"impart of my copending application Serial Number 435,842, filed March-28; 1942; now-"PatentNo. 2,438,267, granted March 2 3, 1948.

Graphiticsteelsare we'll kn'own, and they are now recognized as comprising a-distinct type of steel. .flhesea steel are bhhlncterized, by con- :tainin reez raphiteaaudlbv the; ability o tvelcpsh ehihardness upon appropr ate heat tr atmen filhe noses ighresistan ete abr si n, metal. sickeun, and c rinsr a d hey: a e c assed asbeingrreemachiainer :suchpro rt coupled Mithrdesimble mechanical properties have result dimvcry extensive ,usea i; h er pht steels iomthe making/birdies Qf; many-kinds, punches, 1

innina. slitting and form n r lls, breac es,

and other tools ,uscd for related, purposes, es-

menteor. siliconmnd about 2;.8 percentof tungsten.

grapl'iitic SlSIBClSfkDD-WII'iDIl-DI to'the invenmy: aforesaid :copending, applicationtare hardened by liquidnuenohingri. e.,--.i-nt,0.0i-l,, -Water son brine, nnduncneref those 'earliergaknown graphitic-steels was capable chair-hardening. The necessity. lfnrj harden-insets, ixQUfiMhillfi i aundesirableiin some: ns ances, r s :irrthe '1 case: of warts, oizrnoneuniiprm, section or -of ,relatively smatelengthrand small;sec 0m be a e dis or- EtiQ -l mtltii utlneastaresult,of;quenchin strains.

,nlso nuenchingunraliguid c elant-re uires speccial eeu pment; thesteelsedisclose inrmy oneisal'dfianplicartionfiere i 353 42 l -k wi e;.p ssess rcpelitiesacharac fitistic of graphitic steels bu zareauniqueimtheinabi toibeair hardened.

cmttainitromtabcuw Q-i QPB 'i'QQIIt-QfQCaIP- cam resent; hr mium, abou 0.-'l5,1 te it ners enttots-m n a ese, a outrozsfito 1 per cent of molybdenum, abou 1.

mentmfmtcketraaml abcuteaitaito, r th r-"t *9; silicon,

The .graphitic steels known prior to the present inventionhaveproyed to.be,perfec.t1y satisfactory within their specific fields, and a totalof .many million pounds of them have beenused, However, itischaracteristic ofallof them that, their hardening characteristics are [rather definitely fixedineach case. On theother hand, forsome purposes deep hardening steels are required, as Where the article is subjectedtosevere Wear and can be, reground repeatedly but'is not subject to severe impact. In other casesshallow'hardening is desired to provide a hardened; wearing surface backedIby a softer and, ductile'core. In .view of therather definitely fixed hardeningcharacteristi'cs of thegraphitic steels known prior to this invention they have not been versatile in the sense that. the individual types can .be applied,

according to need, .to satisfy both deep, andshallow hardening. As, a matter of manufacturing and'merchandising practices, and .of economy with respect thereto, it would be dcsirable' on the other hand, to be able to sup ly both deep and shallow, hardening requirements Witha. sin

.gle type analysis, whereby production would be simplified, warehouse stocks could be reduced,

and related advantages gained.

Themajor object of this .inventionis-to provide graphitic steels and articles made therefrom in which the properties characteristic of such steels are combined with controllable hardenability, 1. e., the ability to harden, them shallowly or deeply,'accordin toneed, and whichare of relatively simple and inexpensive composition and do not require the use of large amounts of alloying elements, and which may be air hardened.

Theinvention will be described withreference to the accompanying drawing in which, the

graphs represent the hardening characteristics of twosteels as provided by this invention.

I have discovered, and it islupon this thatrthe present invention is predicated, that ,controllably hardenable graphitic steels are provided b 2 modification of the analysis disclosed and claimed in my. c0pending'applicati0n Ser. No. 435,842, and specifically by loweringsubstantially the content of, nickel, by increasing the upper limit for silicon, and by extending downwardly the lower limit for manganese' 'Desirably .the lower limit of molybdenum is decreasedalso,

Inaccordance with the present invention graphitic' steel articles are made from steels containingabout 1 to 2 per cent of carbon, about 0.255120 1 per centoflchromium, about 0:5,1to per cent of .manganese, about 0.2 to. 1 per cent ofmolybdenum, about 0.25 to 1.4 per centsoihnickel; and about 0.75 to 2 per cent of silicon. "Phosphorus and sulfur should be kept low. The remainder of the steels is iron together with impurities in the amounts customarily encountered in such steels, but it will be understood that other alloy- The controllable hardening characteristic of the steels and articles in accordance with this invention may be exemplified by the following compositions.

Cr Mn 1 Mo Ni Si r I s Per cent Per cent Per cent Per cent Per cent Per cent Per cent Per cent Steel A 1. 45 0. 32 l. 0 0. 26 0. 59 1. 20 0. 016 0. 034 Steel 13 i l. 50 0.53 0. 89 0.45 0.99 1.89 0. 021 0.035

ing elements may be present provided they do not detrimentally affect the properties which characterize the present invention, for which reason the remainder of the steels may be said to be efiectively iron inasmuch as such additional alloying elements do not alter the essential character of products made, in accordance with the present invent-ion.

These steels are productive of articles capable of deep' or shallow hardening, according to the particular composition within th ranges stated, and in all instances they possess the other properties of graphitic steels including mechanical properties, such as tensile strength, elastic limit, and the like, that are requisite and desirable for the purposes to which graphitic steels are applied. Nickel within the range stated results in less austenite than is the case with the steels of Ser. No. 435,842, but it sufiicies to supply adequate mechanical properties through its strengthening effect upon ferrite; also it is ample to efiect the graphitization necessary to p DVide graphitic carbon and to confer adequate harden ing response. 1

In the practice of the invention the desired hardenability, deep or shallow, is obtained by control of the contents of manganese and chromium, which are carbide formers, and of the I graphitizers, molybdenum and nickel, together with silicon. According to the invention deep hardening is obtained by the use of those'five elements toward the upper limits of the ranges stated, which results in relatively high content per cent of graphitic carbon in the case of shallow hardening, and more than about and up to about 0.8 per cent of graphitic carbon indeep hardened steels according to the invention. Of course the compositions are likewise balanced in accordance with known graphitic steel practice, 1. e., so that during hot working the carbon will be wholly or substantially wholly, in the combined state, and so that graphitization will occur upon subsequent annealing. Maximum response to hardening occurs with from about 0.5 to 0.9 per cent of combined carbon. With carbon much in excess of the eutectoid', as is the case with these steels, the presence of excess carbides may retard the formation of austenite during heat treatment, and in the practice of this invention it is generally desirable to balance the composition in such a manner that sufficient or the carbon will be converted to the graphitic state to bring the agraphitic carbon'content close tothe eutectoid. In general, for given contents of Cr,

range is without substantial effect on the harden- The foregoing steels were made in an electric induction furnace and cast into 30-pound ingots which were hot forged to 1% inch rounds which were then subjected to the following annealing (graphitizing) cycle:

Charge at 1000 F.

Heat to 1210 F. at 200/hr. Heat to 1310 F. at P/hr. Heat to 1370 F. at 60/hr. Heat to 1400 F. at 30/hr. Heat to 1430" F. at 10/hr. Hold 6 hours 0001 to 1100 F. Discharge to air Standard end-quench Jominy bars were then machined from the annealed stock, and they were heated for 45 minutes in a neutral salt bath at 1525 F. and quenched in accordance with prescribed Jomin'y practice. The hardnesses determined from the resulting specimens are shown in the accompanying drawing. It will be observed that steel A'is hardenable at /1a inch Jominy distance to Re. 60, showing it to be a shallow hardening steel. In contrast, steel B, containing the same amount of carbon but with greater amounts of alloying elements shows hardenability of 1 /2 inches Jominy distance to Re. 60, which shows this steel to be deep hardening. The markedly different hardening characteristics of these two steels demonstrates clearly how both deep and shallow hardening may be obtained in the practice of this invention. Intermediate results are,.of course, possible. An analysis similar to A but with only 1.15 per cent of carbon showed a Jominy curve essentially the same as that of steel A, which is generally true of these steels The steels provided by this inventionmay be made in accordance with procedures standard in the art for the production of graphitic steels. Preferably they are made in an electric furnace following standard killed steel practice, the various alloying, elements being introduced suitably in the form of ferro-alloys, or otherwise as desired. They are cast in chill molds toavoid. formation of graphite in the ingots.

The ingots are treated prior to and during hot working in a manner understood in the graphitic steel art, 1. e., so that the carbon will :remain substantially entirely in the combined form during hot working. Generally speaking, the'ingots should be hot worker, as by rolling or forging, at a temperature not over about 1950 F. or 2000 F. to produce shapes of desired form and size for conversion into final products. In case it is necessary to forge the hot rolled material to form dies or other tools the hot rolled shapes should be heated slowly to 2000 F. and held until they havebeen' heated through, after which at 20/hr.

they are forged to shape with care taken-that the temperature during forging does not fall below about 1750" F.

V perature for four hours.

subjecting them to normalizing and annealing treatments. To this end they are normalized by heating above the critical range, suitably at about 1700 F., to cause decomposition and diffusion of carbides. They are then cooled, in accordance with ordinary normalizing practice, by being removed from the furnace and cooled in air. Thereafter the articles are annealed by reheating them into or above the critical range, say by heating to 1450 F. and holding at that tem- The articles are then cooled slowly, advantageously at about 20 F. per hour, to below the critical range, after which they are removed from the furnace and allowed to air cool. In this manner the carbides are partially decomposed with production of graphitic carbon and with spheroidization of residual carbides.

Treated in the manner just described, steels of the preferred composition given hereinabove will contain substantial percentages of free graphite, depending on the particular analysis, the re mainder of the carbon being in combined form. The graphitic carbon confers surface lubricating qualities desirable in articles provided by the invention, while the carbides provide, upon suitable heat treatment, high wear resistance and a structure possessing other desirable qualities which are detailed hereinafter. The combination of graphitic carbon and spheroidized carbides also causes the steels in this condition to be easily machinable. It is characteristic of products provided by this invention that the graphitic carbon is dispersed in finely divided form, and uniformly, throughout the structure, and that when hardened they possess remarkable non-seizing qualities.

After being graphitized the articles are machined or otherwise finished to shape and size, after which they are subjected to a hardening treatment in which they are heated above the critical range and air cooled. A variety of structures can be produced, depending upon the conditions of the hardening treatment, Austenitic structures may be produced but it is now preferred for most purposes to conduct such hardening heat treatment to produce an austeniticmartensitic structure. It is particularly desirable to use for that purpose a double hardening procedure. With sections up to, about 2 inches thick, it suflices usually to pack the articles in a suitable compound, heat to 1625" F., then cool in air, and then to reharden at 1550 F. With sections from about 2 inches to 4 inches thick, the first heating should be about 1650 F., while with sections over 4 inches the first hardening should be at about 1675 F. In both cases rehardening is effected at 1550 F. at which temperature the articles are held until heated throughout, the exact time depending, of course, upon their mass. On the first hardening there will be retained a substantial proportion of austenite. The rehardening step is desirable because it gives increased wearing properties resultant from production of martensite by conversion of some of the austenite. Hardnesses of 60 to 65 R0. are regularly obtainable through hardening in the manner described.

The controllable hardenability of the steels provided by this invention and of articles made from them, is highly advantageous for reasons that will be clear to those familiar with the art. A further advantage is that, like the steels of my copending application Ser. No. 435,842, it is possible to effect hardening without distortion of tools of variable section or of considerable length and small section, whose quenching in oil or water is hazardous. Similarly, these steels possess the unusual property of being likewise capable of hardening in oil or water if that is desirable for any reason.

According to the provisions of the patent statutes, I have explained the principle and method of practicing my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1. As a new article of manufacture a hot worked and heat treated alloy steel article formed from steel of controllable hardenability consisting essentially of about 1 to 2 per cent of carbon, about 0.25 to 1 per cent of chromium, about 0.5 to 1.5 per cent of manganese, about 0.2 to 1 per cent of molybdenum, about 0.25 to 1.4 per cent of nickel, about 0.75 to 2 per cent of silicon, and the remainder iron and characterized by austeniticmartensitic structure containing graphitic carbon and spheroidized carbide dispersed finely through the structure, by high resistance to wear, and by being deeply hardened when said elements, other than carbon, are toward the upper limit of the ranges stated, and by being shallow hardened when the said elements, other than carbon, are toward the lower limits of the ranges stated.

2. Alloy steel of controllable hardenability consisting essentially of about 1 to 2 per cent of carbon, about 0.25 to 1 per cent of chromium, about 0.5 to 1.5 per cent of manganese, about 0.2 to 1 per cent of molybdenum, about 0.25 to 1.4 per cent of nickel, about 0.75 to 2 per cent of silicon, and the remainder iron, and characterized by capability of being hot worked and of producing upon heat treatment austenitic-martensitic structures containing graphitic carbon and spheroidized carbide dispersed finely through the structure, and of high resistance to wear, and by being deeply hardening when said elements, other than carbon, are toward the upper limit of the ranges stated, and by being shallow hardening when the said elements, other than carbon, are toward the lower limits of the ranges stated.

3. Shallow hardening steel according to claim 2 containing from 1.15 to 1.45 per cent of carbon, about 0.3 per cent of chromium, about 1 per cent of manganese, about 0.25 per cent of molybdenum, about 0.6 per cent of nickel, and about 1.2 per cent of silicon.

4. Deep hardening steel according to claim 2 containing about 1.5 per cent of carbon, about 0.55 per cent of chromium, about 0.9 per cent of manganese, about 0.45 per cent of molybdenum, about 1 per cent of nickel, and about 1.9 per cent of silicon.

FREDERICK R. BONTE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,253,502 Boegehold Aug. 26, 1941 2,291,842 Strauss Aug. 4, 1942 2,370,225 Boegehold Feb. 27, 1945 2,438,267 Bonte Mar. 23, 1948 

2. ALLOY STEEL OF CONTROLLABLE HARDENABILITY CONSISTING ESSENTIALLY OF ABOUT 1 TO 2 PER CENT OF CARBON, ABOUT 0.25 TO 1 PER CENT OF CHROMIUM, ABOUT 0.5 TO 1.5 PER CENT OF MANGANESE, ABOUT 0.2 TO 1 PER CENT OF MOLYBDENUM, ABOUT 0.25 TO 1.4 PER CENT OF NICKEL, ABOUT 0.75 TO 2 PER CENT OF SILICON, AND THE REMAINDER IRON, AND CHARACTERIZED BY CAPABILITY OF BEING HOT WORKED AND OF PRODUCING UPON HEAT TREATMENT AUSTENITIC-MARTENSITIC STRUCTURES CONTAINING GRAPHITIC CARBON AND SPHEROIDIZED CARBIDE DISPERSED FINELY THROUGH THE STRUCTURE, AND OF HIGH RESISTANCE TO WEAR, AND BY BEING DEEPLY HARDENING WHEN SAID ELEMENTS, OTHER THAN CARBON, ARE TOWARD THE UPPER LIMIT OF THE RANGES STATED, AND BY BEING SHALLOW HARDENING WHEN THE SAID ELEMENTS, OTHER THAN CARBON, ARE TOWARD THE LOWER LIMITS OF THE RANGES STATED. 